As a fluid-pressure apparatus as mentioned above, a hydraulic pump which rotates a pair of gears by an appropriate drive motor and pressurizes an operation fluid by the rotational motions of the gears and discharges the pressurized operation fluid, and a hydraulic motor which rotates gears by introducing a previously pressurized operation fluid therein and uses rotational forces of rotating shafts of the gears as a power are conventionally known.
Such fluid-pressure apparatuses have a problem of operational noise generated by meshing of gears, a problem of noise generated by discontinuous change of the volume of the liquid confined between tooth surfaces of the meshing gears, and the like. In order to reduced such noise, conventionally a fluid-pressure apparatus using a pair of gears having a theoretical tooth profile which prevents the occurrence of a gap between tooth surfaces of the gears meshing with each other has been suggested (see the Unexamined Patent Application (Translation of PCT Application) Publication No. 2010-521610).
FIGS. 8 to 11 show the fluid-pressure apparatus disclosed in the Unexamined Patent Application (Translation of PCT Application) Publication No. 2010-521610, specifically, an oil hydraulic device. It is noted that, although the Unexamined Patent Application (Translation of PCT Application) Publication No. 2010-521610 does not disclose the whole configuration of the oil hydraulic device, FIGS. 8 and 9 shows also the whole configuration thereof.
As shown in FIGS. 8 and 9, an oil hydraulic device 1 has a housing 2 having a hydraulic chamber 4 formed therein, a pair of helical gears 20′, 23′ (hereinafter, simply referred to as “gears”) inserted in the hydraulic chamber 4 in a state where their tooth portions mesh with each other, and bushes 30, 32 as two support members which are inserted in the hydraulic chamber 4 in a state of being in contact with both end surfaces of the pair of gears 20′, 23′ to support the pair of gears 20′, 23′.
The housing 2 comprises a body 3 in which the hydraulic chamber 4 having a space with a substantially 8-shaped cross-section is formed from one end surface to the other end surface thereof, a first flange 8 screwed on the one end surface of the body 3, and a second flange 11 similarly screwed on the other end surface of the body 3, and the hydraulic chamber 4 is closed by the first flange 8 and the second flange 11.
One of the pair of gears 20′, 23′ is a driving gear 20′ and the other is a driven gear 23′. The gears 20′, 23′ respectively have rotating shafts 21, 24 which are respectively provided to extend in the axial directions of the gears 20′, 23′ from both end surfaces of the gears 20′, 23′, and the rotating shaft 21 of the gear 20′ has a tapered portion formed on one end portion thereof and a screw portion 22 is formed on the tip of the tapered portion. Further, the pair of gears 20′, 23′ are, as described above, contained in the hydraulic chamber 4 in a state of meshing with each other, and the outer surfaces of their tooth tips are in sliding contact with an inner peripheral surface 7 of the hydraulic chamber 4.
The bushes 30, 32 are metal bearings comprising a plate-shaped member having a substantially 8-shaped cross-section and respectively have two support holes 31, 33, and the rotating shafts 21, 24 of the gears 20′, 23′ are inserted through the support holes 31, 33, and thereby the rotating shafts 21, 24 are supported to be rotatable. Further, the bushes 30, 32 are inserted in the hydraulic chamber 4 in a state where the rotating shafts 21, 24 of the gears 20′, 23′ are inserted through the support holes 31, 33 and end surfaces of the bushes 30, 32 are in contact with the end surfaces of the gears 20′, 23′. It is noted that the other end surfaces of the bushes 30, 32 are in contact with of end surfaces of the first flange 8 and the second flange 11, respectively, and thereby movement of the gears 20′, 23′ and the bushes 30, 32 in their axial directions is restricted.
Further, the first flange 8 has an insertion hole 9 formed through which the rotating shaft 21 having the screw portion 22 of the driving gear 20′ is inserted, and the driving gear 20′ is arranged in the hydraulic chamber 4 in a state where the rotating shaft 21 is inserted through the insertion hole 9 of the first flange 8 and extended to the outside. Further, an oil seal 10 is provided in the insertion hole 9 and the oil seal 10 provides sealing between the insertion hole 9 and the rotating shaft 21. It is noted that O-rings 12 are respectively interposed between the end surfaces of the body 3 and the first and second flanges 8, 11, and the O-rings 12 provide sealing therebetween.
Further, the body 3 has an intake port (intake flow path) 5, which leads to the hydraulic chamber 4, bored in one side surface thereof and a discharge port (discharge flow path) 6, which similarly leads to the hydraulic chamber 4, bored in another side surface thereof located opposite said side surface with the hydraulic chamber 4 between them. Further, the intake port 5 and the discharge port 6 are provided so that their axes are positioned at the middle between the rotating shafts 21, 24 of the pair of gears 20′, 23′.
The pair of gears 20′, 23′ has such a theoretical tooth profile that their tooth surfaces are continuously and linearly in contact with each other in the axial direction of the rotating shafts 21, 24 and tooth tips of one of them are brought into contact with tooth bottoms of the other of them as shown in FIGS. 10 and 11. Thus, due to the contact between the gears 20′ and 23′, the hydraulic chamber 4 is divided in two, a high-pressure side and a low-pressure side, with the contact portion 26 as a border. The bushes 30, 32 being in contact with the end surfaces of the gears 20′, 23′ have a function of preventing leakage of the operation fluid from the high-pressure side to the low-pressure side by the contact between the gears 20′ and 23′, and therefore, in the oil hydraulic device 1, the roundness or inclination of edges of the end surfaces of the tooth portions of the gears 20′, 23′ is set to be as small as possible.
The oil hydraulic device 1 having the above-described configuration can be used as an oil hydraulic pump or an oil hydraulic motor. For example, in a case where it is used as an oil hydraulic pump, appropriate piping which is connected to an appropriate tank for storing an operation fluid therein is connected to the intake port 5 of the housing 2, and the rotating shaft 21 of the driving gear 20′ is driven by an appropriate drive motor, thereby rotating the driving gear 20′ in the direction indicated by the arrow R shown in FIG. 11.
Thereby, the driven gear 23′ meshing with the driving gear 20′ is rotated in the direction indicated by the arrow R′, the operation fluid in a space 28 between the inner peripheral surface 7 of the hydraulic chamber 4 and the tooth portions of the gears 20′, 23′ is transferred to the discharge port 6 side by the rotation of the gears 20′, 23′, and the discharge port 6 side is brought into a high pressure and the intake port 5 side is brought into a low pressure, with the contact portion 26 between the pair of gears 20′, 23′ as a border.
When the intake port 5 side is brought into a negative pressure in the above-described manner, the operation fluid in the tank is inhaled into the low-pressure side of the hydraulic chamber 4 through the piping and the intake port 5, and is transferred to the discharge port 6 side by the operation of the pair of gears 20′, 23′ and thereby pressurized to a high pressure, and the pressurized operation fluid is discharged through the discharge port 6.
In the above-described manner, the oil hydraulic device 1 functions as an oil hydraulic pump.
Further, according to this oil hydraulic device 1, since, as described above, the pair of gears 20′, 23′ have such a theoretical tooth profile that their tooth surfaces are continuously and linearly in contact with each other in the axial direction of the rotating shafts 21, 24 and the tooth tips of one of them are brought into contact with the tooth bottoms of the other, the above-mentioned noise problems can be solved. Further, since the roundness or inclination of the edges of the end surfaces of the tooth portions is set to be as small as possible and thereby the sealability between the end surfaces of the gears and the end surfaces of the bushes is improved, thereby preventing leakage of the operation fluid from the high-pressure discharge port 6 side to the low-pressure intake port 5 side, high discharge volume (which is volume efficiency and also output efficiency) can be obtained.